Multi-Antenna Scheduling System and Method

ABSTRACT

A wireless communication method and system using virtual MIMO (“V-MIMO”) are provided. Post processing signal to interference and noise ratios (“SINR”) for a plurality of signals corresponding to a plurality of mobile terminals arranged as a V-MIMO group are estimated. The one of the plurality of mobile terminals having the highest post processing SINR is selected. Wireless communication for the selected mobile terminal is scheduled. The signal corresponding to the selected mobile terminal is cancelled. Post processing signal to interference and noise ratios (“SINR”) for the signals corresponding to the remaining mobile terminals is re-estimated. The one of the remaining mobile terminals having the highest post processing SINR is selected. Wireless communication for the selected remaining mobile terminal is scheduled.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/843,098, filed Aug. 22, 2007, entitled MULTI-ANTENNA SCHEDULINGSYSTEM AND METHOD, which is related to and claims priority to U.S.Provisional Application Ser. No. 60/823,196, filed Aug. 22, 2006,entitled MULTI-ANTENNA SCHEDULING SYSTEMS AND METHODS, the entirety ofwhich both are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

FIELD OF THE INVENTION

The present invention relates to wireless network communications andparticular to a method and system for increasing wireless communicationnetwork spectral efficiency in multiple input multiple output (“MIMO”)antenna systems through the use of resource scheduling.

BACKGROUND OF THE INVENTION

Wireless communication networks, such as cellular networks, operate bysharing resources among the mobile terminals operating in thecommunication network. As part of the sharing process, resourcesrelating to assigned channels, codes, etc. are allocated by one or morecontrolling devices within the system. Certain types of wirelesscommunication networks, e.g., orthogonal frequency division multiplexed(“OFDM”) networks, are used to support cell-based high speed servicessuch as those under certain standards such as the 3rd GenerationPartnership Project (“3GPP”) and 3GPP2 evolutions, e.g., Long TermEvolution (“LTE”), the Ultra-Mobile Broadband (“UMB”) broadband wirelessstandard and the IEEE 802.16 standards. The IEEE 802.16 standards areoften referred to as WiMAX or less commonly as WirelessMAN or the AirInterface Standard.

OFDM technology uses a channelized approach and divides a wirelesscommunication channel into many sub-channels which can be used bymultiple mobile terminals at the same time. These sub-channels and hencethe mobile terminals can be subject to interference from adjacent cellsand other mobile terminals because neighboring base stations and mobileterminals can use the same frequency blocks. The result is that spectralefficiency is reduced, thereby reducing both communication throughput aswell as the quantity of mobile terminals that can be supported in thenetwork.

This problem is further exacerbated in multiple input, multiple output(“MIMO”) environments. Multiple Input, Multiple Output OrthogonalFrequency Division Multiplexing (“MIMO-OFDM”) is an OFDM technology thatuses multiple antennas to transmit and receive radio signals. MIMO-OFDMallows service providers to deploy wireless broadband systems that takeadvantage of the multi-path properties of environments using basestation antennas that do not necessarily have line of sightcommunications with the mobile terminal.

MIMO systems use multiple antennas to simultaneously transmit data, insmall pieces to the receiver, which processes the separate datatransmissions and puts them back together. This process, called spatialmultiplexing, can be used to proportionally boost the data-transmissionspeed by a factor equal to the number of transmitting antennas. Inaddition, since all data is transmitted both in the same frequency bandand with separate spatial signatures, this technique utilizes spectrumvery efficiently.

MIMO operation implements a channel matrix (N×M) where N is the numberof transmit antennas and M is the number of receive antennas to definethe coding and modulation matrix for the wireless communication channelas a whole. The less correlated each column in the matrix is, the lessinterference experienced in each channel (as a result of the multipleantennas). In the case where there is a totally uncorrelatedarrangement, i.e., the dot product between columns is zero, the channelsare considered orthogonal to one another. Orthogonality provides theleast antenna-to-antenna interference, thereby maximizing channelcapacity, and data rate due to the higher post-processing signal tointerference and noise ratio (“PP-SINR”). PP-SINR is the SINR after theMIMO decoding stage.

Virtual MIMO (“V-MIMO”) implements the MIMO technique described above byusing multiple simultaneously transmitting mobile terminals each havingone or more antennas. The serving base station includes multipleantennas. Although the base station can treat virtual MIMO operation astraditional MIMO in which a single mobile terminal has multiple antennasand can separate and decode the transmissions from the multiplesimultaneously transmitting mobile terminals, channel correlation amongmobile terminals as discussed above results in channel capacity loss dueto inter-mobile terminal interference. Scheduling the transmissions fromthe multiple mobile terminals to share channel resources can providesystem capacity gain (also referred to as “scheduling gain”). It istherefore desirable to have a virtual MIMO arrangement that maximizessystem capacity through the use of scheduling gain.

It is known that orthogonality-based scheduling can reduce inter-mobileterminal interference. However, this arrangement only works well innarrow-band implementations because the channel characteristics, e.g.,attenuation, phase, etc., do not significantly change because thechannel is almost constant in the frequency band. In other words, thechannel matrix that defines the channel also does not significantlychange. In contrast, wideband diversity channel implementations, such asOFDM, can result in different channel characteristics across thefrequency band. The result is that a wideband diversity channel that isorthogonal at one point does not mean that the channel is orthogonal ata different spot within the channel. Hence, orthogonality basedscheduling is likely ineffective in wideband implementations.

Arrangements for MIMO wideband transmission scheduling are known. Forexample, it is known to schedule MIMO transmission by matching themodulation coding set (“MCS”) of each layer, where a layer is anindependent parallel transmitted data stream, i.e., data streams frommultiple mobile terminals in a virtual MIMO environment, to the channelquality indicator (“CQI”) of that layer. However, using these knowntechniques, the CQI of each layer is computed according to thepost-processing effective SINR, i.e., after spacial processing by thebase station. The undesirable result is that this arrangement isprocessing intensive and does not adequately exploit the channelcapacity. It is therefore further desirable to have a schedulingarrangement that can be implemented in OFDM virtual MIMO environments tosupport, for example, WiMAX communications such that channel capacity isused in as efficient a manner as possible.

SUMMARY OF THE INVENTION

The present invention advantageously provides a method and system forwireless uplink communication in a virtual MIMO environment by usingdecision-based feedback interference cancellation. The use ofdecision-based feedback interference cancellation advantageouslyexploits multi-user gain thereby providing greater wireless channel datathroughput capacity than is possible using currently known techniques.It is noted that the present invention can be implemented inconventional MIMO environments as well.

In accordance with one aspect, the present invention provides a methodfor wireless communication in which post processing signal tointerference and noise ratios (“SINR”) for a plurality of signalscorresponding to a plurality of mobile terminals arranged as a V-MIMOgroup are estimated. The one of the plurality of mobile terminals havingthe highest post processing SINR is selected. Wireless communication forthe selected mobile terminal is scheduled. The signal corresponding tothe selected mobile terminal is cancelled. Post processing signal tointerference and noise ratios (“SINR”) for the signals corresponding tothe remaining mobile terminals is re-estimated. The one of the remainingmobile terminals having the highest post processing SINR is selected.Wireless communication for the selected remaining mobile terminalscheduled.

In accordance with another aspect, the present invention provides awireless communication method in which post processing signal tointerference and noise ratios (“SINR”) for a first signal correspondingto a first mobile terminal and second signal corresponding to a secondmobile terminal arranged as a V-MIMO group are estimated. Wirelesscommunication for the one of the first and second mobile terminalshaving the highest post processing SINR is scheduled. The signalcorresponding to the one of the first and second mobile terminals havingthe highest post processing SINR is cancelled. A post processing signalto interference and noise ratio (“SINR”) for the signal corresponding tothe remaining one of the first mobile terminal and the second mobileterminal is re-estimated. Wireless communication for the remaining oneof the first and second mobile terminals is scheduled.

In accordance with still another aspect, the present invention providesa wireless communication system in which the system has a schedulingdevice. The device includes a central processing unit operating to:

-   -   estimate post processing signal to interference and noise ratios        (“SINR”) for the plurality of signals corresponding to a        plurality of mobile terminals arranged as a virtual MIMO        (V-MIMO) group;    -   select the one of the plurality of mobile terminals having the        highest post processing SINR;    -   schedule wireless communication for the selected mobile        terminal;    -   cancel the signal corresponding to the selected mobile terminal;    -   re-estimate post processing signal to interference and noise        ratios (“SINR”) for the signals corresponding to the remaining        mobile terminals;    -   select the one of the remaining mobile terminals having the        highest post processing SINR; and

schedule wireless communication for the selected remaining mobileterminal.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagram of an embodiment of a system constructed inaccordance with the principles of the present invention;

FIG. 2 is a block diagram of an exemplary base station constructed inaccordance with the principles of the present invention;

FIG. 3 is a block diagram of an exemplary mobile terminal constructed inaccordance with the principles of the present invention;

FIG. 4 is a block diagram of an exemplary OFDM architecture constructedin accordance with the principles of the present invention;

FIG. 5 is a block diagram of the flow of received signal processing inaccordance with the principles of the present invention;

FIG. 6 is a diagram of an exemplary scattering of pilot symbols amongavailable sub-carriers; and

FIG. 7 is a flow chart of an exemplary decision-based feedbackinterference cancellation process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As an initial matter, while certain embodiments may discussed in thecontext of wireless networks operating in accordance with a particularwireless standard, the invention is not limited in this regard and maybe applicable to other broadband networks including those operating inaccordance with wireless standards such as those using OFDM orthogonalfrequency division (“OFDM”)-based systems including WiMAX (IEEE 802.16)and 3rd Generation Partnership Project (“3GPP”) evolution, e.g., LongTerm Evolution (“LTE”), Ultra-Mobile Broadband (“UMB”), etc. Similarly,the present invention is not limited solely to OFDM-based systems andcan be implemented in accordance with other system technologies, e.g.,CDMA.

Referring now to the drawing figures in which like reference designatorsrefer to like elements, there is shown in FIG. 1, a system constructedin accordance with the principles of the present invention anddesignated generally as “6.” System 6 includes one or more base stations8 and one or more mobile terminals 10 (shown as mobile terminals 10 aand 10 b in FIG. 1). Although not shown, mobile terminals 10 cancommunicate with base stations 8 via one or more relay nodes. Basestations 8 communicate with one another and with external networks, suchas the Internet (not shown), via carrier network 12. Base stations 8engage in wireless communication with mobile terminals 10 directly orvia one or more relay nodes. Similarly, mobile terminals 10 engage inwireless communication with base stations 8 directly or via one or morerelay nodes.

Base station 8 can be any base station arranged to wirelesslycommunicate with mobile terminals 10. Base stations 8 include thehardware and software used to implement the functions described hereinto support the V-MIMO transmission scheduling functions. Base stations 8include a central processing unit, transmitter, receiver, I/O devicesand storage such as volatile and nonvolatile memory as may be needed toimplement the functions described herein. Base stations 8 are describedin additional detail below.

Mobile terminals 10, also described in detail below, can be any of awide variety of mobile terminals including, but not limited to, acomputing device equipped for wireless communication, cell phone,wireless data terminal, wireless personal digital assistant (“PDA”) andthe like. Mobile terminals 10 also include the hardware and softwaresuitable to support the functions needed to engage in wireless V-MIMOcommunication with base station 8. Such hardware can include a receiver,transmitter, central processing unit, storage in the form of volatileand nonvolatile memory, input/output devices, etc.

Relay nodes (not shown) are optionally used to facilitate wirelesscommunication between mobile terminal 10 and base station 8 in theuplink (mobile terminal 10 to base station 8) and/or the downlink (basestation 8 to mobile terminal 10). A relay node configured in accordancewith the principles of the present invention includes a centralprocessing unit, storage in the form of volatile and/or nonvolatilememory, transmitter, receiver, input/output devices and the like. Relaynodes also include software to implement the MAC control functionsdescribed herein. Of note, the arrangement shown in FIG. 1 is general innature and other specific communication embodiments constructed inaccordance with the principles of the present invention arecontemplated.

Although not shown, system 6 can include a base station controller(“BSC”) that controls wireless communications within multiple cells,which are served by corresponding base stations (“BS”) 8. It isunderstood that some implementations, such as LTE and WiMAX, do not makeuse of a BSC. In general, each base station 8 facilitates communicationsusing V-MIMO OFDM with mobile terminals 10, which are illustrated asbeing within the geographic confines of the cell 14 associated with thecorresponding base station. Movement of mobile terminals 10 in relationto the base stations 8 can result in significant fluctuation in channelconditions as a consequence of multipath distortion, terrain variation,reflection and/or interference caused by man-made objects (such asbuildings and other structures), and so on.

Multiple mobile terminals 10 may be logically grouped together to form aV-MIMO group 16. Of note, although FIG. 1 shows two mobile terminals 10grouped to form V-MIMO group 16, the invention is not limited to such.It is contemplated that more than two mobile terminals can exist in aV-MIMO group 16. It is also contemplated that a mobile terminal can havemore than one antenna to operate using traditional MIMO for wirelesscommunications as well as participate as part of a V-MIMO group 16. Evenusing diversity channels, where orthogonality-based scheduling isineffective and mobile terminals 10 therefore interfere with each other,mobile terminals 10 can still be paired in accordance with the presentinvention to take advantage of the multi-user gain associated with MIMOwireless communication.

Base station 8 is also shown in FIG. 1 as including 2 antennas 18 tosupport V-MIMO operation. It is understood that the present invention isnot limited to such and that base station 8 can include more than twoantennas 18 or even a single antenna 18 in support of multiple mobileterminals 10. FIG. 1 shows each mobile terminals 10 engaged in wirelesscommunication with each antenna 18 of base station 8.

A high level overview of the mobile terminals 10 and base stations 8 ofthe present invention is provided prior to delving into the structuraland functional details of the preferred embodiments. It is understoodthat relay nodes can incorporate those structural and functional aspectsdescribed herein with respect to base stations 8 and mobile terminals 10as may be needed to perform the functions described herein.

With reference to FIG. 2, a base station 8 configured according to oneembodiment of the present invention is illustrated. The base station 8generally includes a control system 20, a baseband processor 22,transmit circuitry 24, receive circuitry 26, one or more antennas 18,and a network interface 30. The receive circuitry 26 receives radiofrequency signals bearing information from one or more remotetransmitters provided by mobile terminals 10 (illustrated in FIG. 3).Preferably, a low noise amplifier and a filter (not shown) cooperate toamplify and remove out-of-band interference from the signal forprocessing. Down conversion and digitization circuitry (not shown) thendown converts the filtered, received signal to an intermediate orbaseband frequency signal, which is then digitized into one or moredigital streams.

The baseband processor 22 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 22 is generallyimplemented in one or more digital signal processors (“DSPs”) orapplication-specific integrated circuits (“ASICs”). The receivedinformation is then sent across a wireline or wireless network via thenetwork interface 30 or transmitted to another mobile terminal 10serviced by the base station 8.

On the transmit side, the baseband processor 22 receives digitized data,which may represent voice, data, or control information, from thenetwork interface 30 under the control of control system 20, and encodesthe data for transmission. The encoded data is output to the transmitcircuitry 24, where it is modulated by a carrier signal having a desiredtransmit frequency or frequencies. A power amplifier (not shown)amplifies the modulated carrier signal to a level appropriate fortransmission, and delivers the modulated carrier signal to the antennas18 through a matching network (not shown). Modulation and processingdetails are described in greater detail below.

With reference to FIG. 3, a mobile terminal 10 configured according toone embodiment of the present invention is described. Similar to basestation 8, a mobile terminal 10 constructed in accordance with theprinciples of the present invention includes a control system 32, abaseband processor 34, transmit circuitry 36, receive circuitry 38, oneor more antennas 40, and user interface circuitry 42. The receivecircuitry 38 receives radio frequency signals bearing information fromone or more base stations 8. Preferably, a low noise amplifier and afilter (not shown) cooperate to amplify and remove out-of-bandinterference from the signal for processing. Down conversion anddigitization circuitry (not shown) then down convert the filtered,received signal to an intermediate or baseband frequency signal, whichis then digitized into one or more digital streams.

The baseband processor 34 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations, as will be discussed in greater detail below. Thebaseband processor 34 is generally implemented in one or more digitalsignal processors (“DSPs”) and application specific integrated circuits(“ASICs”).

With respect to transmission, the baseband processor 34 receivesdigitized data, which may represent voice, data, or control information,from the control system 32, which the baseband processor 34 encodes fortransmission. The encoded data is output to the transmit circuitry 36,where it is used by a modulator to modulate a carrier signal that is ata desired transmit frequency or frequencies. A power amplifier (notshown) amplifies the modulated carrier signal to a level appropriate fortransmission, and delivers the modulated carrier signal to the antennas40 through a matching network (not shown). Various modulation andprocessing techniques available to those skilled in the art areapplicable to the present invention.

In OFDM modulation, the transmission band is divided into multiple,orthogonal carrier waves. Each carrier wave is modulated according tothe digital data to be transmitted. Because OFDM divides thetransmission band into multiple carriers, the bandwidth per carrierdecreases and the modulation time per carrier increases. Since themultiple carriers are transmitted in parallel, the transmission rate forthe digital data, or symbols, on any given carrier is lower than when asingle carrier is used.

OFDM modulation is implemented, for example, through the performance ofan Inverse Fast Fourier Transform (“IFFT”) on the information to betransmitted. For demodulation, a Fast Fourier Transform (“FFT”) on thereceived signal is performed to recover the transmitted information. Inpractice, the IFFT and FFT are provided by digital signal processingcarrying out an Inverse Discrete Fourier Transform (“IDFT”) and DiscreteFourier Transform (“DFT”), respectively. Accordingly, the characterizingfeature of OFDM modulation is that orthogonal carrier waves aregenerated for multiple bands within a transmission channel. Themodulated signals are digital signals having a relatively lowtransmission rate and capable of staying within their respective bands.The individual carrier waves are not modulated directly by the digitalsignals. Instead, all carrier waves are modulated at once by IFFTprocessing.

In one embodiment, OFDM is used for at least the downlink transmissionfrom the base stations 8 to the mobile terminals 10. Each base station 8is equipped with n transmit antennas 18, and each mobile terminal 10 isequipped with m receive antennas 40. Notably, the respective antennascan be used for reception and transmission using appropriate duplexersor switches and are so labeled only for clarity. FIG. 1 shows n=2 andm=2.

With reference to FIG. 4, a logical OFDM transmission architecture isdescribed according to one embodiment. Initially, the base stationcontroller 10 sends data to be transmitted to various mobile terminals10 to the base station 8. The base station 8 may use the channel qualityindicators (“CQIs”) associated with the mobile terminals to schedule thedata for transmission as well as select appropriate coding andmodulation for transmitting the scheduled data. The CQIs may be provideddirectly by the mobile terminals 10 or determined at the base station 8based on information provided by the mobile terminals 10. In eithercase, the CQI for each mobile terminal 10 is a function of the degree towhich the channel amplitude (or response) varies across the OFDMfrequency band.

The scheduled data 44, which is a stream of bits, is scrambled in amanner reducing the peak-to-average power ratio associated with the datausing data scrambling logic 46. A cyclic redundancy check (“CRC”) forthe scrambled data is determined and appended to the scrambled datausing CRC adding logic 48. Next, channel coding is performed usingchannel encoder logic 50 to effectively add redundancy to the data tofacilitate recovery and error correction at the mobile terminal 10.Again, the channel coding for a particular mobile terminal 10 is basedon the CQI. The channel encoder logic 50 uses known Turbo encodingtechniques in one embodiment. The encoded data is then processed by ratematching logic 52 to compensate for the data expansion associated withencoding.

Bit interleaver logic 54 systematically reorders the bits in the encodeddata to minimize the loss of consecutive data bits. The resultant databits are systematically mapped into corresponding symbols depending onthe chosen baseband modulation by mapping logic 56. Preferably,Quadrature Amplitude Modulation (“QAM”) or Quadrature Phase Shift Key(“QPSK”) modulation is used. The degree of modulation is preferablychosen based on the CQI for the particular mobile terminal. The symbolsmay be systematically reordered to further bolster the immunity of thetransmitted signal to periodic data loss caused by frequency selectivefading using symbol interleaver logic 58.

At this point, groups of bits have been mapped into symbols representinglocations in an amplitude and phase constellation. When spatialdiversity is desired, blocks of symbols are then processed by space-timeblock code (“STC”) encoder logic 60, which modifies the symbols in afashion making the transmitted signals more resistant to interferenceand more readily decoded at a mobile terminal 10. The STC encoder logic60 will process the incoming symbols and provide n outputs correspondingto the number of transmit antennas 18 for the base station 8. Thecontrol system 20 and/or baseband processor 22 will provide a mappingcontrol signal to control STC encoding. At this point, assume thesymbols for the n outputs are representative of the data to betransmitted and capable of being recovered by the mobile terminal 10.See A. F. Naguib, N. Seshadri, and A. R. Calderbank, “Applications ofspace-time codes and interference suppression for high capacity and highdata rate wireless systems,” Thirty-Second Asilomar Conference onSignals, Systems & Computers, Volume 2, pp. 1803-1810, 1998, which isincorporated herein by reference in its entirety.

For the present example, assume the base station 8 has two antennas 18(n=2) and the STC encoder logic 60 provides two output streams ofsymbols. Accordingly, each of the symbol streams output by the STCencoder logic 60 is sent to a corresponding IFFT processor 62,illustrated separately for ease of understanding. Those skilled in theart will recognize that one or more processors may be used to providesuch digital signal processing, alone or in combination with otherprocessing described herein. It is further envisioned that processingfunctionality can likewise be consolidated into a lesser number ofprocessors than referenced herein. The IFFT processors 62 willpreferably operate on the respective symbols to provide an inverseFourier Transform. The output of the IFFT processors 62 provides symbolsin the time domain. The time domain symbols are grouped into frames,which are associated with a prefix by like insertion logic 64. Each ofthe resultant signals is up-converted in the digital domain to anintermediate frequency and converted to an analog signal via thecorresponding digital up-conversion (DUC) and digital-to-analog (D/A)conversion circuitry 66. The resultant (analog) signals are thensimultaneously modulated at the desired RF frequency, amplified, andtransmitted via the RF circuitry 68 and antennas 18. Notably, pilotsignals known by the intended mobile terminals 10 are scattered amongthe sub-carriers. The mobile terminals 10, which are discussed in detailbelow, will use the pilot signals for channel estimation.

Reference is now made to FIG. 5 to illustrate reception of thetransmitted signals by a mobile terminal 10. Upon arrival of thetransmitted signals at each of the antennas 40 of the mobile terminal10, the respective signals are demodulated and amplified bycorresponding RF circuitry 70. For the sake of conciseness and clarity,only one of the receive paths is described and illustrated in detail, itbeing understood that a receive path exists for each antenna 40.Analog-to-digital (“A/D”) converter and down-conversion circuitry 72digitizes and downconverts the analog signal for digital processing. Theresultant digitized signal may be used by automatic gain controlcircuitry (“AGC”) 74 to control the gain of the amplifiers in the RFcircuitry 70 based on the received signal level.

Initially, the digitized signal is provided to synchronization logic 76,which includes coarse synchronization logic 78, which buffers severalOFDM symbols and calculates an auto-correlation between the twosuccessive OFDM symbols. A resultant time index corresponding to themaximum of the correlation result determines a fine synchronizationsearch window, which is used by fine synchronization logic 80 todetermine a precise framing starting position based on the headers. Theoutput of the fine synchronization logic 80 facilitates frameacquisition by frame alignment logic 84. Proper framing alignment isimportant so that subsequent FFT processing provides an accurateconversion from the time to the frequency domain. The finesynchronization algorithm is based on the correlation between thereceived pilot signals carried by the headers and a local copy of theknown pilot data. Once frame alignment acquisition occurs, the prefix ofthe OFDM symbol is removed with prefix removal logic 86 and resultantsamples are sent to frequency offset correction logic 88, whichcompensates for the system frequency offset caused by the unmatchedlocal oscillators in the transmitter and the receiver. Preferably, thesynchronization logic 76 includes frequency offset and clock estimationlogic 82, which is based on the headers to help estimate such effects onthe transmitted signal and provide those estimations to the correctionlogic 88 to properly process OFDM symbols.

At this point, the OFDM symbols in the time domain are ready forconversion to the frequency domain using FFT processing logic 90. Theresults are frequency domain symbols, which are sent to processing logic92. The processing logic 92 extracts the scattered pilot signal usingscattered pilot extraction logic 94, determines a channel estimate basedon the extracted pilot signal using channel estimation logic 96, andprovides channel responses for all sub-carriers using channelreconstruction logic 98. In order to determine a channel response foreach of the sub-carriers, the pilot signal is essentially multiple pilotsymbols that are scattered among the data symbols throughout the OFDMsub-carriers in a known pattern in both time and frequency. FIG. 6illustrates an exemplary scattering of pilot symbols among availablesub-carriers over a given time and frequency plot in an OFDMenvironment. Referring again to FIG. 5, the processing logic comparesthe received pilot symbols with the pilot symbols that are expected incertain sub-carriers at certain times to determine a channel responsefor the sub-carriers in which pilot symbols were transmitted. Theresults are interpolated to estimate a channel response for most, if notall, of the remaining sub-carriers for which pilot symbols were notprovided. The actual and interpolated channel responses are used toestimate an overall channel response, which includes the channelresponses for most, if not all, of the sub-carriers in the OFDM channel.

The frequency domain symbols and channel reconstruction information,which are derived from the channel responses for each receive path areprovided to an STC decoder 100, which provides STC decoding on bothreceived paths to recover the transmitted symbols. The channelreconstruction information provides equalization information to the STCdecoder 100 sufficient to remove the effects of the transmission channelwhen processing the respective frequency domain symbols

The recovered symbols are placed back in order using symbolde-interleaver logic 102, which corresponds to the symbol interleaverlogic 58 of the transmitter. The de-interleaved symbols are thendemodulated or de-mapped to a corresponding bitstream using de-mappinglogic 104. The bits are then de-interleaved using bit de-interleaverlogic 106, which corresponds to the bit interleaver logic 54 of thetransmitter architecture. The de-interleaved bits are then processed byrate de-matching logic 108 and presented to channel decoder logic 110 torecover the initially scrambled data and the CRC checksum. Accordingly,CRC logic 112 removes the CRC checksum, checks the scrambled data intraditional fashion, and provides it to the de-scrambling logic 114 forde-scrambling using the known base station de-scrambling code to recoverthe originally transmitted data 116.

Referring again to FIG. 1, in accordance with the present invention,scheduling can be combined with digital signal processing to provide athroughput gain when compared with known techniques. As is discussedbelow in detail, this gain can be realized by pairing a high SINR mobileterminal 10 with a low SINR mobile terminal 10 to form a V-MIMOarrangement, and using decision-based feedback interferencecancellation. Decision-based feedback interference cancellation is usedto remove the signal corresponding to the high SINR mobile terminal 10to facilitate detection of the low SINR mobile terminal 10. Where morethan two mobile terminals 10 are part of V-MIMO group 16, the signalsfor mobile terminals 10 can be iteratively removed beginning with thehighest SINR mobile terminal 10. Low SINR mobile terminals 10 aretypically present at the cell 14 edge, thereby consuming significantbattery power during transmission. The scheduling method of the presentinvention advantageously provides quick and efficient transmissionscheduling, thereby minimizing the unnecessary wasted consumption ofbattery power.

As is discussed below in detail, the present invention, throughscheduling and decision-based feedback interference cancellation allowsresources to be scheduled in a manner that adapts the data rate, i.e.,the adaptive modulation coding (“AMC”) scheme, to the channel quality.In other words, the present invention allows one to establish as high amodulation and coding rate for the capability of the channel as isreasonably possible. This arrangement is described as follows.

Initially, it is noted that multi-user sharing of a communicationchannel, such as in a V-MIMO environment, does not change the overallcapacity of the wireless communication channel. Assume system 6 has twotransmitting sources, such as mobile terminals 10 a and 10 b,transmitting signals s₁ and s₂, respectively, having power P₁ and P₂,respectively where P₁>P₂, and noise signal n₀ having power P_(n). Inthis case, the received signal “r” can be written as r=s₁+s₂+n₀. If s₂is treated as Gaussian noise, i.e., interference, when s₁ is decoded,the result is that the channel capacity, C₁, for mobile terminal 10 a isC₁=log₂(1+P₁/(P₂+P_(n))). If s₁ can be successfully decoded andsubtracted from “r” by base station 8, the remaining capacity withrespect to mobile terminal 10 b, i.e., s₂, is C₂=log₂(1+P₂/P_(n)). Assuch, total channel capacity “C” is C₁+C₂ which equalslog₂(1+(P₁+P₂/P_(n))). Accordingly, there is no loss of total channelcapacity in the face of multi-mobile terminal 10 sharing.

The preceding example is based on the assumption that s₂ is treated asGaussian noise. However, in traditional MIMO systems, s₂ is not treatedas Gaussian noise. Rather, minimum mean square error (“MMSE”)interference suppression or maximum likelihood (“ML”) detection is used.These techniques employ interference cancellation using spectralprocessing. In accordance with these techniques, channel capacity C₁ isactually much higher than in the Gaussian noise assumption methoddescribed above. As a result, it is shown that the use of interferencecancellation results in channel gain in a multi-mobile terminal 10environment. This channel gain can be leveraged through the use ofscheduling and efficient interference cancellation.

The present invention leverages the multi-mobile terminal gain byiteratively scheduling the stronger layer, i.e., independent mobileterminal 10 data stream, based on the post-processing effective SINR. Inaccordance with one embodiment, this scheduling is done by base station8. Scheduling in the context of the present invention includes assigninga modulation coding set (“MCS”). The weaker layer(s) are theniteratively scheduled as if the stronger layer does not exist. Theresult is that there is much higher throughput in the weaker second (andlower) layers as compared with known techniques. Because the weakerlayer is typically power limited, the improved scheduling methodologyprovides power and diversity gain for the weaker layer(s). Of course, itis understood that the determination of which layer is the strongestresults, at least in part, on the MCS assigned by scheduling basestation 8 to mobile terminal 10. The scheduling base station 8 candetermine which mobile terminal 10 uses the interference-free channel.Although this determination is typically based on CQI, it can also bebased on quality of service (“QoS”).

It is also noted that, although a particular layer might first appearstronger than another, that layer may turn out to be weaker when astronger layer is cancelled. For example, if three layers A, B and C arepresent and initial strength measurements reveal that A is thestrongest, B is the second strongest and C is the weakest, it may turnout during subsequent iterative measurements that C is actually strongerthan B when layer A is cancelled.

As noted above, cancellation in accordance with the present inventionoccurs at the receiver, i.e., base station 8. This cancellation isdecision-based feedback interference cancellation (“DFIC”). Inaccordance with the present invention, Turbo decoding of each layer isdone serially and is done after interference cancellation in order toavoid unnecessary decoding. The decoding order is based on thescheduling of the mobile terminals 10 which itself is based on DFIC.This arrangement yields performance increases over known wirelesstransmission schemes with respect to both system throughput, e.g.,channel capacity, and receiver complexity. The scheduler of the presentinvention exploits the multi-mobile terminal channel gain discussedabove.

An exemplary decision-based feedback interference cancellation processconstructed in accordance with the principles of the present inventionis described with reference to FIG. 7. The process is explained withrespect to base station 8. However, it is understood that other devicesin system 6 can be used to perform the below-described schedulingprocess. Initially, using the measured received noise power on aper-antenna basis and using the V-MIMO channel matrix (“H”) stored bybase station 8, the post processing SINR (“PP-ESNR”) for each mobilestation 10 in V-MIMO group 16 is estimated (step S100). By way ofnon-limiting example, the channel matrix “H” can be formed by receivingpilot signals from the mobile terminals 10, estimating the channels fromthese mobile terminals 10 using the received pilot signals and formingthe channel matrix “H” from these estimated channels.

The mobile terminal 10 k_(m) having the largest PP-ESNR is scheduled,i.e., assigned an MCS based at least in part on the measured SINR (stepS102). If there are more mobile terminals 10 in V-MIMO group 16 (stepS104), the columns in the V-MIMO channel matrix “H” corresponding tomobile terminal 10 k_(m) are removed (step S106) and the resultantmatrix “H” stored. The PP-ESNR is then re-estimated for the remainingchannels (step S108) and the process returns to step S102 for thesubsequent scheduling of the remaining mobile terminal(s) 10. As isreadily observable, this subsequent scheduling is based on the cancelledsignal (it is considered interference.) of the higher SINR mobilestations 10.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

1. A wireless virtual multiple input multiple output (“MIMO”)communication method, comprising: estimating post processing signal tointerference and noise ratios (“SINR”) for a plurality of signalscorresponding to a plurality of mobile terminals arranged as a virtualMIMO group; selecting a first mobile terminal of the plurality of mobileterminals, the first mobile terminal having the highest estimated postprocessing SINR; scheduling wireless communication for the first mobileterminal; re-estimating post processing SINR for signals correspondingto the plurality of mobile terminals excluding the first mobile terminalwith the signal corresponding to the first mobile terminal beingcancelled for the re-estimation; selecting a second mobile terminal ofthe plurality of mobile terminals, the second mobile terminal having thehighest post processing SINR according to the re-estimation; andscheduling wireless communication for the second mobile terminal.
 2. Themethod of claim 1, wherein scheduling wireless communication comprisesassigning a modulation coding set.
 3. The method of claim 1, wherein thesignal corresponding to the first mobile terminal is cancelled duringthere-estimation by performing decision-based interference cancellation.4. The method of claim 1, further comprising performing turbo decodingon the signal corresponding to the second mobile terminal.
 5. The methodof claim 1, further comprising storing values corresponding to thesignals received from the plurality of mobile terminals as a channelmatrix.
 6. The method of claim 5, wherein the signal corresponding tothe first mobile terminal is cancelled during the re-estimation byremoving columns corresponding to the first terminal from the channelmatrix.
 7. The method of claim 1, wherein an order of decoding signalsis based on an order in which signals are scheduled. 8 and
 9. (canceled)10. The method of claim 1, wherein the method is performed by a networkelement selected from a group consisting of a base station, a relay anda mobile terminal.
 11. A wireless virtual multiple input multiple output(“MIMO”) communication system, comprising: a receiver configured toreceive a plurality of signals corresponding to a plurality of mobileterminals; and circuitry coupled to the receiver, configured to:estimate post processing signal to interference and noise ratios(“SINR”) for the plurality of signals corresponding to the plurality ofmobile terminals arranged as a virtual MIMO group; select a first mobileterminal of the plurality of mobile terminals, the first mobile terminalhaving the highest estimated post processing SINR; schedule wirelesscommunication for the first mobile terminal; re-estimate post processingSINR for signals corresponding to the plurality of mobile terminalsexcluding the first mobile terminal with the signal corresponding to thefirst mobile terminal being cancelled for the re-estimation; select asecond mobile terminal of the plurality of mobile terminals, the secondmobile terminal having the highest post processing SINR according to there-estimation; and schedule wireless communication for the second mobileterminal.
 12. The system of claim 11, wherein said scheduling thewireless communication comprises assigning a modulation coding set. 13.The system of claim 11, wherein the circuitry is configured to cancelthe signal corresponding to the first mobile terminal during there-estimation by performing decision-based interference cancellation.14. The system of claim 11, wherein the circuitry is configured toperform turbo decoding on the signal corresponding to the second mobileterminal.
 15. The system of claim 11, wherein circuitry is configured tostore values corresponding to the signals received from the plurality ofmobile terminals as a channel matrix.
 16. The system of claim 15,wherein the circuitry is configured to cancel the signal correspondingto the first mobile terminal during the re-estimation by removingcolumns corresponding to the first terminal from the channel matrix. 17.The system of claim 11, wherein the circuitry is configured to order adecoding of signals based on an order in which the signals arescheduled. 18-22. (canceled)
 23. The system of claim 11, wherein thesystem comprises a base station.
 24. The system of claim 11, wherein thesystem comprises a mobile station.
 25. The system of claim 11, whereinthe system comprises a relay station.
 26. A non-transitory, computeraccessible memory medium storing program instructions for performingwireless virtual multiple input multiple output (“MIMO”) communication,wherein the program instructions are executable by a processor to:estimate post processing signal to interference and noise ratios(“SINR”) for a plurality of signals corresponding to a plurality ofmobile terminals arranged as a virtual MIMO group; select a first mobileterminal of the plurality of mobile terminals, the first mobile terminalhaving the highest estimated post processing SINR; schedule wirelesscommunication for the first mobile terminal; re-estimate post processingSINR for signals corresponding to the plurality of mobile terminalsexcluding the first mobile terminal with the signal corresponding to thefirst mobile terminal being cancelled for the re-estimation; select asecond mobile terminal of the plurality of mobile terminals, the secondmobile terminal having the highest post processing SINR according to there-estimation; and schedule wireless communication for the second mobileterminal.
 27. The non-transitory, computer accessible memory medium ofclaim 26, wherein scheduling wireless communication comprises assigninga modulation coding set.
 28. The non-transitory, computer accessiblememory medium of claim 26, wherein the signal corresponding to the firstmobile terminal is cancelled during the re-estimation by performingdecision-based interference cancellation.
 29. The non-transitory,computer accessible memory medium of claim 26, wherein the programinstructions are further executable to: perform turbo decoding on thesignal corresponding to the second mobile terminal.
 30. Thenon-transitory, computer accessible memory medium of claim 26, whereinthe program instructions are further executable to: store valuescorresponding to the signals received from the plurality of mobileterminals as a channel matrix.
 31. The non-transitory, computeraccessible memory medium of claim 30, wherein the signal correspondingto the first mobile terminal is cancelled during the re-estimation byremoving columns corresponding to the first terminal from the channelmatrix.
 32. The non-transitory, computer accessible memory medium ofclaim 25, wherein an order of decoding signals is based on an order inwhich signals are scheduled.